NUCLEAR-MAGNETIC-RESONANCE STUDIES OF SILICON(IV) COMPLEXES IN AQUEOUS-SOLUTION .1. TRIS-CATECHOLATO COMPLEXES

Quantitative data for the reaction 3LH2+Si(OH)4 ⇌ SiL2-3+4H2O in aqueous solution have been obtained by 1H and 29Si NMR spectroscopy, where LH2 = catechol, 4,5-dichlorocatechol, 4-nitrocatechol or 3,4-dinitrocatechol. By a suitable choice of LH2 it is possible to obtain stable solutions of tris-catecholato complexes of silicon(IV), in the presence of Si(OH)4, at pH values ranging from alkaline to as low as 4.1. When LH2 = 2,3-dihydroxybenzaldehyde or tiron, meridional and facial isomers have been characterized. Mixed complexes containing catechol and 4-nitrocatechol or catechol and 4,5-dichlorocatechol have also been studied. Information has been obtained about the rate of SiO bond breaking from the 1H NMR spectra of the tris-complex derived from gallic acid. © 1990.